Why does these expressions 2 (30x-24), 3 (20x-16), and 4 (15x-12) have the same expansion?

The expressions have the same expansion I'd say because the pairs 2 and 30, 3 and 20, and 4 and 15 because they are all equivalent to 60 because they are all factors of 60.

Same goes with the other pairs, because they are all equivalent to 48 because they are all factors of 48.